This invention relates to a method of extending at least the lifetime of a Christmas tree or an umbilical. More particularly, it relates to a method of extending at least the lifetime of a Christmas tree or an umbilical, the Christmas tree being provided with a high-pressure hydraulic valve package and a low-pressure hydraulic valve package. The invention also includes a device for practising the method.
During the recovery of petroleum offshore, it has turned out that there is a need to exceed the originally intended technical-economic life of well equipment. This also applies to safety-critical components such as a Christmas tree with associated valves and control apparatuses.
A Christmas tree located on the seabed has often been guided onto a production tubing head via guide posts. The Christmas tree communicates with equipment on the surface via a so-called umbilical which may typically comprise cables for electric power and signals, optical fibres for signal transmission, pipes for hydraulic fluid under high pressure and low pressure and pipes for the supply of chemicals. It is common for the Christmas tree to be provided with a valve cap which forms a barrier between the annulus, the production bore and the surroundings. The valve cap must be removed when suitable tools that are provided with connections for liquids that are used for the removal of scale and for well-killing are to be installed.
The terms high pressure and low pressure are not exact, as they vary between the different suppliers. Roughly speaking, a pressure between 100 and 300 bars is characterized as a low pressure whereas a pressure above 300 bars is characterized as a high pressure. By pressures below 100 bars, actuators and valves may take a so-called “fail safe” position, which will often shut down the petroleum production.
The hydraulic fluids are typically carried to, respectively, a high-pressure valve package and a low-pressure valve package on the Christmas tree, the high-pressure valve package communicating with a downhole safety valve, whereas the low-pressure valve package communicates with, among other things, a number of actuators principally for valve control in the Christmas tree.
Electric power and control signals are carried to a submerged control module on or at the Christmas tree. The control module which is controlled from the surface is connected to the different hydraulic valves in the valve packages, thereby controlling the different valve functions in the Christmas tree.
Known Christmas tree installations exhibit in particular two weaknesses which emerge after a long time in operation. The control module is prone to functional faults while, at the same time, the availability of new control modules of the kind in question, and also of spare parts therefore, is limited.
The umbilical with associated components is prone to leakages.